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(11) | EP 2 790 281 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Spark plug |
| (57) In order to improve the welding strength between a ground electrode and a noble metal
tip, a spark plug is equipped with an insulating body having an axial hole that penetrates
in the axial direction, a center electrode disposed at the tip of the axial hole,
a substantially tubular main fitting that holds the insulating body, a ground electrode
having one end attached to the end of the main fitting and the other end facing the
tip of the center electrode, and a noble metal tip that is disposed on the surface
of the ground electrode facing the tip of the center electrode and that forms a spark
discharge gap between the tip and the center electrode. The melting of the ground
electrode and the noble metal tip forms a fused section on at least one portion of
the area between the ground electrode and the noble metal tip. If the thickness of
the part of the fused section that is the thickest in the axial direction is set as
(A) and the length of the part of the fused section that is the longest in the longitudinal
direction of the ground electrode is set as (B), the spark plug satisfies the following
relationship: 1.5 ≤ B/A.
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